1. Field of the Invention
The present invention relates to an apparatus for measuring a shape of an object, and more particularly to an apparatus for measuring a shape of an object, by means of shooting a beam of light on the object and forming a silhouette image of the object.
2. Description of the Prior Arts
In order to increase productivity, inspection of bend shapes of bent bars or pipes is required to be performed in a short time. The inspection has been hitherto carried out through visual observation by an inspector by means of inspection tools. This way of inspection has a drawback in that there is not a little possibility of missing a defect at the time of inspection, and the quality of products cannot be fully guaranteed. In addition, there has been also difficulty in feeding back the results of the inspection to change operation conditions of a bending machine, even if shape defects of bent bars or pipes are found. This is because the visual observation is not performed quantitatively. Owing to these disadvantages, automation of shape inspection of bent bars or pipes has been strongly demanded.
To overcome these disadavantages, an apparatus for evaluating the bend shape of bent bars or pipes is disclosed, as prior art, in Japanese Patent Application Laid Open (KOKAI) No. 132856/76, which comprises:
(a) a pair of image formation devices having optical systems, each, composed of an optical axis approximately at a right angle to the longitudinal axis of an objective bar to be measured, and of a light source and a light receiving unit confronted each other to allow, the objective bare to be in between them so that the optical systems may be arranged to cross at right angles each other;
(b) said pair of the image formation devices being set in plurality and in a direction of the longitudinal axis of the objective bar; and
(c) means for converting intensity pattern of light, at an image formation position of each of said image formation devices, into an electric signals and means for calculating bending shape, based on the electric signals.
This prior art apparatus is applicable to those bars which have such a small bending curve as to be regarded almost as linear and still are satisfactory for inspection if deviation of those bars are sampled at several points in the longitudinal direction. However, this apparatus has a drawback in that it is not applicable to those bars having large bending curves and, furthermore, a number of bending portions. This is because:
(l) shape deviation must be measured in every point of a bent bar;
(m) depending on bend shape, an axis of the bend bar forms an angle almost parallel to an optical axis of optical systems; and
(n) depending on bend shape, two or more points of the bend bar are formed overlappedly on a receiving unit as well.